curl_easy_pause.3 5.2 KB

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  22. .TH curl_easy_pause 3 "17 Dec 2007" "libcurl 7.18.0" "libcurl Manual"
  23. .SH NAME
  24. curl_easy_pause - pause and unpause a connection
  25. .SH SYNOPSIS
  26. .B #include <curl/curl.h>
  27. .BI "CURLcode curl_easy_pause(CURL *"handle ", int "bitmask " );"
  28. .SH DESCRIPTION
  29. Using this function, you can explicitly mark a running connection to get
  30. paused, and you can unpause a connection that was previously paused.
  31. A connection can be paused by using this function or by letting the read or
  32. the write callbacks return the proper magic return code
  33. (\fICURL_READFUNC_PAUSE\fP and \fICURL_WRITEFUNC_PAUSE\fP). A write callback
  34. that returns pause signals to the library that it couldn't take care of any
  35. data at all, and that data will then be delivered again to the callback when
  36. the writing is later unpaused.
  37. While it may feel tempting, take care and notice that you cannot call this
  38. function from another thread. To unpause, you may for example call it from the
  39. progress callback (\fICURLOPT_PROGRESSFUNCTION(3)\fP), which gets called at
  40. least once per second, even if the connection is paused.
  41. When this function is called to unpause reading, the chance is high that you
  42. will get your write callback called before this function returns.
  43. The \fBhandle\fP argument is of course identifying the handle that operates on
  44. the connection you want to pause or unpause.
  45. The \fBbitmask\fP argument is a set of bits that sets the new state of the
  46. connection. The following bits can be used:
  47. .IP CURLPAUSE_RECV
  48. Pause receiving data. There will be no data received on this connection until
  49. this function is called again without this bit set. Thus, the write callback
  50. (\fICURLOPT_WRITEFUNCTION(3)\fP) won't be called.
  51. .IP CURLPAUSE_SEND
  52. Pause sending data. There will be no data sent on this connection until this
  53. function is called again without this bit set. Thus, the read callback
  54. (\fICURLOPT_READFUNCTION(3)\fP) won't be called.
  55. .IP CURLPAUSE_ALL
  56. Convenience define that pauses both directions.
  57. .IP CURLPAUSE_CONT
  58. Convenience define that unpauses both directions.
  59. .SH RETURN VALUE
  60. CURLE_OK (zero) means that the option was set properly, and a non-zero return
  61. code means something wrong occurred after the new state was set. See the
  62. \fIlibcurl-errors(3)\fP man page for the full list with descriptions.
  63. .SH LIMITATIONS
  64. The pausing of transfers does not work with protocols that work without
  65. network connectivity, like FILE://. Trying to pause such a transfer, in any
  66. direction, will cause problems in the worst case or an error in the best case.
  67. .SH AVAILABILITY
  68. This function was added in libcurl 7.18.0. Before this version, there was no
  69. explicit support for pausing transfers.
  70. .SH "USAGE WITH THE MULTI-SOCKET INTERFACE"
  71. Before libcurl 7.32.0, when a specific handle was unpaused with this function,
  72. there was no particular forced rechecking or similar of the socket's state,
  73. which made the continuation of the transfer get delayed until next
  74. multi-socket call invoke or even longer. Alternatively, the user could
  75. forcibly call for example \fIcurl_multi_socket_all(3)\fP - with a rather hefty
  76. performance penalty.
  77. Starting in libcurl 7.32.0, unpausing a transfer will schedule a timeout
  78. trigger for that handle 1 millisecond into the future, so that a
  79. curl_multi_socket_action( ... CURL_SOCKET_TIMEOUT) can be used immediately
  80. afterwards to get the transfer going again as desired.
  81. .SH "MEMORY USE"
  82. When pausing a read by returning the magic return code from a write callback,
  83. the read data is already in libcurl's internal buffers so it'll have to keep
  84. it in an allocated buffer until the reading is again unpaused using this
  85. function.
  86. If the downloaded data is compressed and is asked to get uncompressed
  87. automatically on download, libcurl will continue to uncompress the entire
  88. downloaded chunk and it will cache the data uncompressed. This has the side-
  89. effect that if you download something that is compressed a lot, it can result
  90. in a very large data amount needing to be allocated to save the data during
  91. the pause. This said, you should probably consider not using paused reading if
  92. you allow libcurl to uncompress data automatically.
  93. .SH "SEE ALSO"
  94. .BR curl_easy_cleanup "(3), " curl_easy_reset "(3)"